108 



FOREST INFLUENCES. 



the open fails to reacli tlie gauges under tlio trees. Taking all seasons 

 together this deficit under trees is 25 per cent. The disposal of this 

 water is easy to explain. It does not include the water that drips from 

 trees, for this is fairly accounted for by the ganges. It is the water which 

 moistens the tree and its various parts, and also that which flows down 

 the trunk. The latter part reaches the soil and is measurable ; theformer 

 is evaporated again without reaching the soil. At ^"aucy arraugements 

 were made for including in the catch of the gauge the part which flows 

 down the trunk. At two stations large gauges were put in; they were 

 of the same size as the tree crown and they embraced the trunk, a collar 

 about which directed the water into the recei\'er of the gauge. The 

 percentage of catch in the woods was here 92, the largest in stations 

 provided with ordinary gauges. The latter were used at the Belle- 

 fontaine station, which was not very distant, and the catch was here 84 per 

 cent. This is larger than for most other reported returns, but the difler- 

 ence between this value and that for Cinq-Franchees may perhaps be 



Fig. 50.— Precipitation through trees at Ciuq Franch^ea and Bellefontaine. 



taken as an approximation to the quantity of rainfoll which flows down 

 the tree trunk. This would be 8 per cent. These are means from eleven 

 years of observation. Fig. 5G gives the distribution of the percent- 

 ages through the year. The upper curve is for Cinq-Franchees with 

 its large rain gauge; the lower curve is for Bellelbntaine with ordinary 

 gauges. They both show something of the dip for the warm season. 

 At Cinq-Franchees the precipitation under trees for one month (Febru- 

 ary) is slightly larger than that in open fields. 



M. Fautrat's observations include those on precii»itation above forests. 

 The rain gauge over the forest was compared with one at the same 

 height and a thousand feet away, over fields. The two pairs of stations 

 were in the forests of Halatte and Ermenonville, and have been already 

 described. The accessible data were, for Halatte, the monthly values 

 for February to July, 1874, and August, 1876, to July, 1877; for Ermen- 

 onville, the monthly values from 1875 to July, 1877. These have been 

 changed into inches and condensed into the accompanying table: 



